The present invention relates to a variable displacement swash-plate compressor.
Japanese Laid-Open Patent Publication No. 52-131204 discloses a conventional variable displacement swash-plate compressor (hereinafter, referred to as a compressor). The compressor includes a swash plate chamber, cylinder bores, a suction chamber, and a discharge chamber, which are provided in the housing. A drive shaft is rotationally supported in the housing. The swash plate chamber accommodates a swash plate, which is rotational through rotation of the drive shaft. The swash plate has a through hole. A link mechanism is located between the drive shaft and the swash plate. The link mechanism allows the inclination angle of the swash plate to be changed. The inclination angle is the angle of the swash plate in relation to a direction perpendicular to the axis of the drive shaft. Each cylinder bore reciprocally accommodates a piston. A conversion mechanism reciprocates each of the pistons in the associated one of the cylinder bores by the stroke corresponding to the inclination angle through rotation of the swash plate. A top dead center associated part for positioning each piston at the top dead center is defined on the swash plate. The inclination angle of the swash plate is changed by an actuator. The actuator is controlled by a control mechanism. The control mechanism includes a pressure regulation valve.
The link mechanism includes a lug member, a hinge ball, and a link. The lug member is located in the swash plate chamber and is fixed to the drive shaft. The hinge ball is fitted about the drive shaft to be arranged in the through hole of the swash plate. This causes the outer circumferential surface of the hinge ball to contact the through hole. The link is provided between the lug member and the swash plate. The link connects the swash plate to the lug member, so that the swash plate is permitted to pivot.
The actuator includes the lug member, a movable body, and a control pressure chamber. The movable body has a cylindrical shape. The movable body is fitted about the drive shaft to be arranged between the lug member and the hinge ball. When the movable body and the hinge ball contact each other, the movable body is engaged with the swash plate via the hinge ball. When moving along the drive shaft axis, the movable body changes the inclination angle of the swash plate. The control pressure chamber, which is defined by the lug member and the movable body, uses its internal pressure to move the movable body.
In this compressor, when the control mechanism connects the discharge chamber and the control pressure chamber with each other using the pressure regulation valve, the pressure in the control pressure chamber is increased. This moves the movable body along the axis of the drive shaft and pushes the hinge ball along the axis of the drive shaft. Accordingly, the hinge ball is moved along the axis of the drive shaft, and the swash plate slides on the hinge ball in the direction reducing the inclination angle. This allows the displacement of the compressor per rotation of the drive shaft to be reduced.
However, in the above described compressor, the movable body of the actuator and the swash plate are engaged with each other via the hinge ball. Thus, the size of the entire compressor needs to be increased to increase the size of the movable body so that the movable body is easily moved with a great thrust.
When decreasing the inclination angle of the swash plate in the compressor, the movable body pushes the swash plate via the hinge ball. The tolerance during manufacture is likely to vary contacting positions between the outer circumferential surface of the hinge ball and the swash plate. Accordingly, when the movable body pushes the hinge ball, the direction of the load acting on the swash plate is likely to change. Thus, the movable body cannot smoothly move the hinge ball along the axis of the drive shaft, and the movable body cannot stably decrease the inclination angle of the swash plate. Also, the orientation of the movable body tends to be unstable, which can result in pressure leakage in the control pressure chamber. In this case, the displacement cannot be quickly changed in response to changes in the driving state of machinery on which the compressor is mounted, such as a vehicle, and high controllability cannot be achieved.